1. Field of the Invention
The present invention relates in general to variable valve actuation devices of an internal combustion engine, and more particularly to the variable valve actuation devices of a type that induces an open/close operation of engine valves (viz., intake and/or exhaust valves) while varying a lift degree of the engine valves in accordance with an operation condition of the engine.
2. Description of the Related Art
Hitherto, in the field of variable valve actuation devices of an internal combustion engine, various types have been proposed and put into practical use. Some of them are described in Japanese Laid-open Patent Applications (Tokkaihei) 7-63023 and 11-107725.